Conventionally, in an output voltage or output signal output from a switching power supply or other electronic equipment, noise of the operating frequency of the electronic equipment and the like and its harmonic frequencies may become mixed. Because the noise may adversely affect external electronic equipment, it is necessary to reduce the noise as needed. When an output voltage of a predetermined voltage value is output by the switching operation of a power transistor in the switching power supply, noise of the switching frequency and its harmonic frequencies may be generated by the switching of current paths as the power transistor is turned on and off, depending on the output rating. It is conceivable that the noise may become superposed on the output voltage and be carried to the external electronic equipment. Particularly, when the switching power supply is mounted in an automobile, the noise of the switching frequency and its harmonic frequencies may become superposed on an audio signal and the like, depending on the switching frequency. As a result, the problem of adverse influence on listening or viewing, or the so-called radio noise, may be caused. In order to reduce the noise, an output noise reducing device equipped with an inductance element, such as a choke coil, may be inserted in the output path of the output voltage and the like (such as in Patent Literature 1).